This invention relates to engines for model aircraft, and particularly, to exhaust control systems for model aircraft engines. More particularly, the present invention relates to throttle and muffler systems for use with model aircraft engines in small radio-controlled model helicopters.
Model aircraft engines typically include a carburetor for mixing air and fuel, an ignition source (e.g., a glow plug), a piston cylinder where the air and fuel are combusted, and an engine exhaust port where engine exhaust from the combusted air and fuel exits the model aircraft engine. Sometimes a muffler is provided to quiet the exhaust gas produced by the model aircraft engine.
A throttle is provided on some model aircraft engines so that a pilot may operate the model aircraft engines at more than one speed. As the model aircraft engine changes speed, the power produced by the model aircraft engine also changes. Adjusting the throttle of the model aircraft engine adjusts the power produced by the model aircraft engine so that the speed at which the helicopter climbs and/or travels may be changed. Throttles are generally situated adjacent to the model aircraft engine inlet to restrict the amount of air entering the carburetor or situated adjacent to the engine exhaust port of the model aircraft engine to restrict the amount of air exiting the engine exhaust port.
The operating speed of most modern throttled model aircraft engines is adjusted by restricting the amount of air entering the carburetor. The primary function of the carburetor, however, is to mix air and fuel. Thus, adding a throttle to the carburetor makes the carburetor considerably more complex. Carburetor-type throttles are also relatively bulky and expensive.
Model aircraft engines can also be throttled by means of a conventional exhaust restrictor throttle mechanism. Exhaust restrictor throttle mechanisms throttle model aircraft engines by restricting the flow of exhaust gas out of engine exhaust ports formed in the model aircraft engine. This method of throttling is particularly advantageous for model aircraft engines including glow plugs because heat is retained within the model aircraft engine piston cylinder to keep the glow plug element hot. In addition, restricting the engine exhaust port also reduces the noise level of exhaust gases exiting the engine. Exhaust restrictor throttles tend to muffle engine noise when engine speed is low, as would be expected on a model helicopter when hovering a few feet above the ground.
Typically, conventional exhaust restrictor throttle mechanisms are of the rotary valve type and are situated immediately adjacent to the model aircraft engine exhaust port. Not only does the exhaust restrictor throttle valve in this location become extremely hot, but the choice and orientation of exhaust restrictor throttle valve configurations is limited by the proximity of the model aircraft engine to a valve-actuation mechanism which actuates the exhaust restrictor throttle valve.
Engine throttling is an important function for the proper operation of model helicopters. While a great deal of interest for flying model helicopters exists in the modeling community, radio-controlled model helicopters are typically expensive and complicated. Only a very small percentage of modelers can actually afford to buy a helicopter and fewer modelers are skillful enough to build and fly a model helicopter successfully.
Recent advances in the art of small radio-controlled model helicopters have resulted in a new class of improved small model helicopters that are simple and inexpensive enough to appeal to a wide modeling audience. New features that are incorporated into this new class of improved small model helicopters to simplify and/or reduce the expense of radio-controlled model helicopters and increase the availability of model helicopters to a wider, less sophisticated audience are disclosed, for example, in U.S. Pat. Nos. 5,305,968 to Paul E. Arlton, 5,597,138 to Paul E. Arlton and David J. Arlton, 5,628,620 to Paul E. Arlton, and 5,609,312 to Paul E. Arlton and David J. Arlton, U.S. patent application Ser. Nos. 08/687,649 by Paul E. Arlton, 08/729,184 by Paul E. Arlton and David J. Arlton, 08/728,929 by Paul E. Arlton, David J. Arlton, and Paul Klusman, 08/814,943 by Paul E. Arlton, and 08/855,202 by Paul E. Arlton and David J. Arlton, and U.S. Provisional Patent Application No. 60/028590 by Paul E. Arlton and Paul Klusman.
Effective speed control of the model aircraft engines for this new class of small model helicopters is problematic, however, because most small model aircraft engines lack throttles. While conventionally throttled model aircraft engines are currently available, these conventional model aircraft engines are typically too large, heavy, powerful, or expensive for the new small radio-controlled model helicopters. Without a throttle, the model aircraft engine provided in most small model aircraft can operate at only one speed.
One type of small model aircraft engine (a Cox.TM. 0.051 engine) currently used on small model helicopters has an exhaust restricting sleeve appended to the piston cylinder to block the exhaust ports and throttle the model aircraft engine. This Cox.TM. model aircraft engine does not include a muffler which makes this model aircraft engine relatively loud and annoying. In addition, this Cox.TM. model aircraft engine does not include a proper exhaust stack to direct oily engine exhaust away from the helicopter which makes the Cox.TM. model aircraft engine messy.
What is needed is a simple, effective mechanism to control the speed of, quiet the exhaust gas produced by, and direct the exhaust gas away from a model aircraft engine for use on small model helicopters. Model helicopter pilots would greatly appreciate a quieter, cleaner, speed-controlled model aircraft engine for use on a small model helicopter.
According to the present invention, an exhaust control mechanism is provided for use in a model engine system having a source of engine exhaust. The exhaust control mechanism includes first and second tubes and a valve movable in one of the first and second tubes. The first tube includes an upper portion, a lower portion, and a first passage extending through the upper portion and lower portion. The upper portion of the first tube is adapted to couple to a source of engine exhaust. The second tube is coupled to the first tube and the second tube is formed to include a second passage that intersects the first passage formed in the first tube at an intersection region. The valve is movable in one of the first and second tubes to extend into the intersection region.
The exhaust control mechanism combines a throttle with an exhaust control member body to control the speed of a model aircraft engine by restricting the passage of exhaust gasses from exhaust ports of the model aircraft engine, quiet the exhaust gasses as they exit the model aircraft engine, and direct the exhaust gasses away from the model aircraft engine. The present invention also provides means for actuating the throttle without introducing a bellcrank into a throttle control linkage extending between the throttle and a throttle servo.
More specifically, the muffler of the exhaust control mechanism includes a chamber body formed to include an exhaust collection chamber communicating with the exhaust ports of the model aircraft engine. In a preferred embodiment, the exhaust collection chamber is sized to operate as an expansion-type muffler. Exhaust gasses produced by the model aircraft engine collect in the exhaust collection chamber and then exit the exhaust collection chamber through an exhaust passage formed in one of the first and second tubes.
The throttle includes an exhaust-restricting mechanism that is movable through a passage formed in one of the first and second tubes and a portion of the other tube to restrict the flow of exhaust gasses through the exhaust control member body thereby controlling the speed and power of the model aircraft engine. In a preferred embodiment, the exhaust-restricting mechanism includes a simple slide valve that translates through the first and second passages. This slide valve includes only one moving part and is oriented to translate through one of the first and second passages inline with the throttle control linkage for simple side-operation of the exhaust-restricting mechanism.
In another alternative embodiment of the present invention, the slide valve may be replaced with a rotary valve, but with the disadvantage of increased part-count. Advantageously, with both slide valve orientations and types of valves, the tube through which exhaust gas flows is unobstructed and extendible (as with silicone tubing) so that exhaust gasses can be routed away from the model aircraft engine and aircraft.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.